PISCES. 
fislies. Of these the most important is re- 
spiration, which is performed by means of 
gills, which supply the place of lungs. Air 
is equally necessary to the existence of fish 
as it is to other animals. In general, a fish 
first receives a quantity of water by the 
mouth, from which it is driven to the gills ; 
these close, and prevent the water from re- 
turning by the mouth, at the same time 
that their bony covering prevents it from 
passing through them, until the proper quan- 
tity of air has been extracted from it. The 
covers tlien open, and give it a free passage ; 
by which means the gills are again opened, 
and admit a fresh body of water. This pro- 
cess, ill fishes, as breathing in the human 
subject, is carried on during sleep, and is 
repeated about twenty-five times in a mi- 
nute ; and the necessity of it is evinced from 
the circumstance of fish being certainly 
killed in water, from which air is taken 
away by means of the air-pump, or exclu- 
ded by very severe frost. Should the 
free play of the gills be even suspended, or 
their covers kept from moving, by a string 
tied round them, the fish would fall into 
convulsions, and die in a few minutes. It 
is said, likewise, that though the branchial 
apparatus be comprized in a small compass, 
its surface when fully extended would oc- 
cupy many square feet ; a fact, that may 
convince the most sceptical, of the number- 
less convolutions and ramifications in which 
the included water is elaborated and atte- 
nuated, in the course of giving out its air 
in the respiratory process. 
Fishes have the organs of sense, some of 
them probably in a very high degree, and 
others imperfectly ; of the latter kind are 
the senses of touch and of taste : but the 
sense of hearing has now been completely 
ascertained, which was long doubted, and 
by some physiologists denied : the organ is 
contained in the cavity of the head ; it was 
discovered by Professor Camper, who re- 
marks, that “ fish perceive sound, but 
sound peculiar to the watery element.” 
This organ has been observed and described 
by Mr. Hunter, in the Philosophical Trans- 
actions, who has likewise ascertained that 
its structure varies in different species. 
And Dr. Shaw, in his “ Introduqtion to the 
Natural History of Fishes,” Vol. iV. Part I. 
observes, that “ Fishes, particularly of the 
skate kind, have a bag at some distance 
behind the eyes, which contains a fluid, and 
a soft cretaceous substance, and supplies 
the place of the vestibule and cochlea : 
there is a nerve distributed upon it similar 
to the portio mollis in man : they have semi- 
circular canals, which are filled with a fluid, 
and communicate with the bag ; they have 
likewise a meatus externus, which leads to 
the internal ear. The cod-fish, and others 
of the same shape, have an organ of hear- 
ing somewhat similar to the former, but in- 
stead of a soft substance contained in the 
bag, there is a hard cretaceous stone.” 
From the same work we shall transcribe the 
observations on the sense of smelling and 
that of sight. 
“ The organ of smelling is large, and the 
animals have a power of contracting and di- 
lating the entry to it as they have occasion. 
It seems to be mostly by their acute smell 
that they discover their food, for their 
tongue seems not to have been designed for 
a very nice sensation, being of a pretty 
firm cartilaginous substance ; and common 
experience evinces that their sight is not of 
so much use to them as their smell in search- 
ing for their nourishment. If you throw a 
fresh worm into the water, a fish shall dis- 
tinguish it at a considerable distance ; and 
that this is not done by the eye, is plain 
from observing, that after the same worm 
has been a considerable time in the water, 
and lost its smell, no fishes will come near 
it ; but if you take out the bait, and make 
several little incisions into it, so as to let 
out more of the odoriferous effluvia, it shall 
have the same effect as- formerly. Now it 
is certain, that had the animals discovered 
this bait with their eyes, they would have 
come equally to it in both cases. In con- 
sequence of their smell being the principal 
means they have of discovering their food, 
we may frequently observe them allowing 
themselves to be carried down with the 
stream, that they may ascend again leisurely 
against the current of the water: thus the 
odoriferous particles swimming in that me- 
dium, being applied more forcibly to their 
organs of smell, produce a stronger sensa- 
tion. 
“ The optic nerves in fishes are not con- 
founded with one another in their middle 
progress between their origin and the orbit, 
but the one passes over the other without 
any communication ; so that the nerve which 
comes from the left side of the brain goes 
distinctly to the right eye, and vice versa. 
Indeed it should seem not to be necessary 
for the optic nerves of fishes to have the 
same kind of connection with each other as 
those of man have; for their eyes are not 
placed in the fore-part, but in the sides of 
the head ; and, consequently, cannot look 
